1. Field of the Invention
The present invention relates to a control system and method for hybrid vehicles, and in particular, to a control system and method for accelerating the warm-up operation for hybrid vehicles.
2. Description of the Related Art
Conventionally, hybrid vehicles employing an engine and a motor as driving sources are known. Among these, in parallel hybrid vehicles, the output of the engine is assisted by driving the motor.
More specifically, when such a parallel hybrid vehicle is accelerated, the engine output is assisted by driving the motor, and when decelerated, various controls such as battery charging using deceleration regeneration are performed so as to maintain a necessary remaining battery charge and also to satisfy the driver's intention. In addition, the parallel hybrid vehicle has a structure in which the engine and the motor are serially arranged; thus, the structure can be simplified so that the total weight of the system can be reduced and the engine and the motor can be flexibly arranged in the vehicle.
In such hybrid vehicles, an ignition timing retarding technique is known (refer to Japanese Unexamined Patent Application, First Publication No. Hei 11-173175, or the like), in which when the warm-up operation (for warming up the vehicle) is started, the ignition timing is retarded (or delayed) so as to accelerate the warm-up operation. According to such a retarding process, the ignition efficiency is lowered, and thermal energy corresponding to a loss owing to the decrease of the ignition efficiency accelerates the warm-up operation.
However, in the above conventional technique, when the ignition timing retarding process is performed, the combustion efficiency is degraded in comparison with the case in which the engine is driven at an optimum ignition timing.
In order to solve this problem, the ignition timing retarding process may be executed for a shorter time. However, in this case, the time for completing the warm-up operation is unnecessarily prolonged, and in particular, if a relatively high idling engine speed is defined during the warm-up operation, the fuel consumption is increased.